The present invention relates to a disposable body warmer, and, more particularly, to a disposable body warmer which has a good rising characteristic (i.e. the rising in temperature is fast), can maintain the temperature a suitable duration, can avoid bulging of a bag and agglomeration of the heat-generating agent after the beginning of use, i.e. during use, and can use a permeable inner bag having a low water vapor permeability.
A disposable body warmer comprises an air-permeable bag, and a mixture contained in the bag and comprising metal powder such as iron powder available at a relatively low cost and assistants such as water, wood flour and sodium chloride. The disposable body warmer utilizes an exothermic reaction caused by supplying oxygen thereto, and is easy to carry and can be easily used by merely opening an outer bag, so that it occupies a major proportion of body warmers in these days.
Further, in order to make the application of the above-mentioned disposable body warmer to the human body easy and simple, there is proposed a disposable body warmer in which an intransferable self-adhesive layer functioning as a conventional attaching means such as an attaching band and a pocket is employed (refer to, for example, Japanese Examined Utility Model Publication No. 34735/1981).
However, when the disposable body warmer of the adhesion type described above is applied to the human body, there are problems that distribution of contents in a bag becomes uneven (such uneven distribution is particularly significant when the body warmer is applied to the human body in a perpendicular or inclined state), and heat generation is completed at an early stage in one part of the heat-generating agent so that heat distribution of the body warmer becomes uneven. There are further problems that partial extreme increase in thickness of a bag, agglomerated heat-generating agent and the like deteriorates the touch and gives unpleasantness (gives inferior feeling in use) to a user.
In order to solve the problems mentioned above, there is proposed a disposable body warmer in which air permeability of one surface of an inner bag containing the heat-generating agent is controlled to reduce the pressure in the bag (refer to, for example, Japanese Examined Utility Model Publication No. 30169/1989 or Japanese Unexamined Patent Publication No. 149272/1990).
The above-mentioned disposable body warmer, however, has problems that (1) there is scatter in performance of the body warmer because air permeability of the inner bag is evaluated based on air permeability per unit time (Japanese Industrial Standard P 8117 hereinafter, Japanese Industrial Standard being abbreviated as JIS), not water vapor permeability (JIS Z 0280) having a high accuracy, (2) usable inner bags are limited to those having air permeability of 5000 to 10000 sec/100 cc, (3) assistants for preventing agglomeration are not employed in the contents, so that agglomeration of the heat-generating agent cannot be avoided unless not less than 9% by weight of water-holding material is added to the heat-generating agent, and (4) the rise-time is long.
It is an object of the present invention to provide a disposable body warmer capable of solving the above-mentioned drawbacks. That is, an object of the present invention is to provide a disposable body warmer which requires a short time to raise its temperature up to a predetermined temperature just from the beginning of heat generation, has a suitable duration for various kinds of uses and is free from bulging and agglomeration of the heat-generating agent after the beginning of use thereof.